Molybdenum is a versatile transition metal that finds uses in such diversified reactions as petroleum hydrodesulfurization, organic oxidations, hydrogenations, coal liquefaction, solar energy conversion, nitrate reduction and nitrogen fixation among others. The unfortunate feature about many of these reactions is that the actual role that the molybdenum plays is unclear. This makes it difficult to modify the molybdenum complex to improve its catalytic behavior. Well characterized molybdenum coordination complexes are needed so that detailed complex structure-reactivity correlations can be established. The purpose of this research is to gain a fuller understanding of the chemistry of Mo in the +4, +5, and +6 oxidation states. New Mo coordination complexes will be synthesized involving changes in (a) oxidation state, (b) coordination number, (c) ligand donor atom set, and (d) coordination geometry. In addition, reactivity patterns will be established for Mo coordination complexes anchored to polymer and electrode supports. A variety of rather simple compounds (PR3, NO3-, RN=NR, alkynes, etc.) are available for evaluating the reactivity of the Mo complexes. Trends in redox potentials, stability, electronic and EPR spectra, and reactivity toward substrates will be established as a function of the parameters (a,b,c,d) listed above. This research is designed to bring about a clearer understanding of the relationship between the ligand structure and reactivity of Mo coordination complexes. Through careful ligand design (including polymer-anchored ligands) the reactivity of Mo complexes can be enhanced. The systematic examination of a large number of Mo complexes in various oxidation states will help to clarify our understanding of the unique chemistry of this metal. The correlations that will develop as the project proceeds will help us to understand more fully the role that Mo plays and how its reactivity can be enhanced in important chemical reactions.